Friday, January 7, 2011

Who You Gonna Call? Mythbusters! BUM BUM BUM BUM

In this lab, we decided to make physics extra extra fun... By using Mythbusters, my group had to bust two myths. It was a challenge, but in the end, victory was ours. We busted those bad boys. Now watch and learn.

Myth 1: An object always moves in the direction of the net force exerted on it.

First Reaction: This isn't required to write this but it is interesting. At first, when you look at the myth you think "uhh duhhh..." because your mind immediately thinks of a force applied. But, once you start analyzing this experiment and taking all of the other forces into the equation your mindset changes.

Prediction: If an object always moves in the direction of the net force exerted on it, then, by hitting the ball in the air it will prove it wrong because the net force is negative and the ball continues to move in a positive direction.

Procedure: Now, this was not the most complicated thing ever. All I had to do was hit the baseball up in the air. While I hit, Matt recorded, and then we analyzed the recording in order to see if our prediction was correct.


Equations for when I hit the ball:

Equations for after I hit the ball:

Outcome: Now, the myth states that an object always moves in the direction of the net force exerted on it. But.... it doesn't. Let's take a look. The ball is moving up and away from me after I hit it. If you were to pause the video after the ball leaves my bat you would see that air resistance and gravity are both in a negative direction. So, if the myth is true, my ball would be moving right back at me to hit me in the head. But, thank goodness, it did not hit me in the head. The ball continued up, positive, and away from me, positive. So, by comparing the FBD's to the video it is clearly shown that even though the net force is negative, the ball is moving in a positive direction. BUSTED!

Myth 2: An object always changes its motion if there is a force exerted on it by other objects.

First Reaction: Your first reaction when you see this myth is puzzling. You are trying to think of a way to bust it, but you are over thinking it. All you have to do is think simple. Most people would think about pushing a wall or something like that, but all you have to think about is simply a tennis ball being hit by a string. Just something small. Now let's see what we did.

Prediction: If an object always changes its motion if there is a force exerted on it by other objects, then, by having me run into Blaine, we will prove it wrong because my motion continues in the same direction.

Procedure: Again, quite an easy procedure. All I do is run into Blaine while Matt records the video. Then we analyze our video and decide if it is busted.


Equations as I hit Blaine:

Outcome: Ok, so, this myth states that an object always changes its motion if there is a force exerted on it by other objects. In our lab, I was the object in motion, and Blaine was the other object exerting a force on me. I was running at him, and then as I made contact the force applied from him was exerted on me. But even though he was applying a force on me, I continued in the same direction. So our lab straight up proves this lab busted. Another object exerted a force on me and my motion continued in the same direction. Myth number 2.... YOUR BUSTED!

Conclusion: We busted both of these myths. We know that they are definitely not true in every situation because in our experiments, they were wrong. But, if we did not bust the myth, it wouldn't necessarily mean that the myth is true. To prove something true, there must be no possible wrong scenarios, and with only one test you could not prove it 100% true.
Like I said earlier, everyone, even I, had first impressions of these myths. In myth 1, you're going to assume of course that if the net force is positive the object moves in a positive direction and if it is negative then a negative direction. It just sounds right if you don't sit down and think about all of the factors, you must know what is going on with the object at all time and that the net force is not always the same. The net force in an objects motion may change, and the motion may change. So, you cannot just eyeball this myth and assume that it is true. As for the second myth, I believe that the only reason why this myth could be misunderstood is just because of the way we live today. We will compare this myth to car wrecks or running into walls (hopefully nobody has run into a wall lately). For this myth you have to think of a scenario where it is big object versus little object or strong object versus weak object because sometimes, this myth can be correct, but it is not always, because we BUSTED it. Busting both of these myths was really fun. I enjoyed proving these easily misunderstood concepts wrong. It helped me understand why people seem to misunderstand it, and now I have enough knowledge to explain to people why this myth is untrue.

Well... that is it for this episode of Mythbusters. So next time there are some physics myths... WHO YOU GONNA CALL? MYTHBUSTERS!!!!



  1. Great job! Neatly explained and fabulous video editing!
    Please copy your posting into a document to spot a few typos that need to be fixed.

  2. Regarding the first 'myth', it is worded improperly, and the word 'moves' should be replaced with 'accelerates', as is so stated by Newton's laws of motion. Even so, if it would be in the direction of the net force exerted on the object, it would still be true do to the fact that net force accounts for all of the nonzero forces acting on the object regardless of direction.

    Regarding the second, after 'is' should be 'an external unbalanced force.' as is stated by Newton's Law of Inertia. If a box is sitting on the ground, the force of Earth's gravity is negated by the ground's normal force. There is more than one force acting on the box. Thus according to your 'myth', the box should be moving. Sure you 'disproved' the myth though it was improperly worded. Should I stop using 'quotes'? Maybe. Good day to you sir.